The present invention relates to an apparatus and method for communication networks that comprise multiple layers, for example wherein the different layers comprise different switching technologies or different switching granularity levels. These networks are commonly known as multi-layer networks (MLN) and multi-region networks (MRN). In such networks a Generalised Multi-Protocol Label Switching (GMPLS) technology, for example, can be provided to support the control of the network.
Most of the initial efforts to utilize GMPLS have been related to environments hosting devices with a single switching capability. The complexity raised by the control of such data planes is similar to that seen in classical IP/MPLS networks. By extending MPLS to support multiple switching technologies, GMPLS provides a comprehensive framework for the control of a multi-layered network of either a single switching technology or multiple switching technologies.
Internet Engineering Task Force (IETF) request for comments (RFC) 5212 defines the concept of multi-region and multi-layer networks, and describes the framework and requirements of GMPLS controlled multi-region and multi-layer networks. In GMPLS, a switching technology domain defines a region, and a network of multiple switching types is referred to in IETF RFC 5212 as a multi-region network (MRN). When referring in general to a layered network, which may consist of either single or multiple regions, IETF RFC 5212 uses the term multi-layer network (MLN).
The GMPLS extensions for multi-region networks and multi-layer networks, including routing aspects and signalling aspects, are described in IETF RFC 6001.
An “edge node” of a region, as described in RFC 5212, is defined as having multiple Interface Switching Capabilities (ISCs). As such, an edge node contains multiple matrices which may be connected to each other by internal links.
Nodes with multiple Interface Switching Capabilities are further classified as “simplex” or “hybrid” nodes by IETF RFC 5212 and IETF RFC 5339. A simplex node advertises several Traffic Engineering (TE) links, each with a single ISC value carried in a sub Time-Length-Value (sub-TLV) of its Interface Switching Capabilities Descriptor (ISCD). A hybrid node advertises a single TE link containing more than one ISCD, each with a different ISC value.
From a signalling point of view, a multi-layer path can be computed and set up basically according three main models:
According to a first model, known as “Pre-provisioning of Forwarding Adjacency Label Switched Paths (FA-LSPs)”, the FA-LSP in a server layer is created before initiating the signalling of the client layer LSP.
According to a second model, known as “Signalling trigger server layer path computation”, a source node of the client layer LSP (or the client layer Path Computation Element, PCE) only computes the route in its layer network. When the signalling of the client layer LSP reaches the region edge node, the edge node performs server layer FA-LSP path computation and then creates the FA-LSP.
According to a third model known as “Full path computation at source node (or Multi-Layer PCE)”, the source node of the client layer LSP (or a PCE), having a multi-layer visibility, performs a full path computation including the client layer and the server layer routes. The server layer FA-LSP creation is triggered at the edge node by the client layer LSP signalling.
In this context, IETF RFCs 4206 and 6107 describe how to set up a hierarchy LSP (H-LSP) passing through multi-layer networks. The basic concept is to create the so called Forwarding Adjacencies (FAs), that is, to create so called Forwarding Adjacency LSPs (FA-LSP) in server layer networks and advertise them as TE links in client layer networks via GMPLS signalling and routing protocols.
In order to achieve these goals, a set of Time-Length-Value objects for Resource Reservation Protocols—Traffic Engineering (RSVP-TE TLV objects) are defined, that enable the exchange of TE Link information between the endpoints of the associated lower layer LSP, thus exploiting the FA-LSP concept. Examples are: the local TE link identifier, the Interior Gateway Protocol (IGP) identifier, and so on.
FIG. 1 shows a new C-Type variant of the LSP_TUNNEL_INTERFACE_ID object that has been defined in this context, to carry an unnumbered interface identifier and to indicate into which instance of the IGP the consequent TE link should be advertised (this last information is specified in specific IGP Instance Identifier TLV).
An important part of this new variant of the LSP_TUNNEL_INTERFACE_ID object, the basic form having been introduced in IETF RFC 3477, is the “Actions” field which is associated in the TLV describing the local TE link identifier, as shown in FIG. 2. The Actions Field consists of a set of flags that specify how the LSP that is being set up has to be treated.
The H-LSP extensions proposed in IETF 6107 are an efficient instrument to set up LSPs in heterogeneous technology networks, but only in simple cases (where there is no ambiguity to identify the layer where the FA-LSP is set and the layer in which the corresponding TE-link is advertised. However, such extensions are not suitable when crossing different layers, and lead to a lack of flexibility for the provision of certain features on a per layer basis.
In other words, there are cases in which it is not possible to provide a lower layer LSP with additional/modified features and/or modify the existing ones, because the required information is not signalled to the region boundary.
In fact, according to the policies of some operators, in a heterogeneous technology it is possible to create LSPs that require additional features when crossing a particular technology due to its specific issues, without impacting the other technologies/layers. This is not possible with the existing extensions described above.